This disclosure is generally directed to printheads for inkjet printing and, more specifically, to printheads modified with a self-assembly monolayer (SAM). This disclosure also relates to processes for making and using the printheads as well as processes for forming patterns and images on a substrate using the printheads.
Inkjet printing is known, but the full capabilities of inkjet printing have not yet been explored. Particularly, the field of printed electronics is a realm capable of benefiting from the implementation of inkjet printing technology.
Ink jetting devices are known in the art, and thus extensive description of such devices is not required herein. As described in U.S. Pat. No. 6,547,380 (Smith et al.), which is hereby incorporated herein by reference in its entirety, ink jet printing systems are generally of two types: continuous stream and drop-on-demand.
Inkjet printing of electronics is described in U.S. Pat. No. 5,972,419 (Roitman) as well as in U.S. Pat. No. 7,176,040 (Sirringhaus, et al.), both of which are hereby incorporated by reference herein in their entirety.
U.S. Pat. No. 6,336,697 (Fukushima) discloses a liquid jetting structure with a flow path inside a nozzle that is set to have a degree of affinity for a jetted liquid that changes in the direction of the liquid flow.
U.S. Pat. No. 6,444,318 (Guire et al.), which is hereby incorporated by reference herein in its entirety, discloses a surface coating composition for providing a SAM, in stable form, on a material surface.
U.S. Pat. No. 6,872,588 (Chabinyc et al.) discloses a semiconductor processing method and fabrication methods for large-area arrays of thin film transistors.
U.S. Pat. No. 7,105,375 (Wu et al.) discloses a method of patterning organic semiconductor layers of electronic devices using reverse printing.
U.S. Pat. No. 7,282,735 (Wu et al.), the disclosure of which is totally incorporated herein by reference, discloses a thin film transistor having a fluorocarbon-containing layer which may be a SAM layer.
The deposition of functional materials such as semiconductor, conductor and/or insulating materials using inkjet processes can significantly lower manufacturing costs. However, to manufacture electrical circuits with a sufficient resolution, high printing accuracy of the printed functional materials is very important. Because the functional material formulations, such as semiconductor inks, often contain organic solvents, the inks normally exhibit low surface tension and are therefore sensitive to surface energy variation in the printing surface of the printhead and undesirable ink deposition on the printing surface of the printhead. This sensitivity results in printing issues such as misdirectional deposition of ink drops (or poor accuracy), which results in an inferior product. The present inventors believe that the misdirectional deposition of the ink may be due to accumulation of materials around the printing orifice and/or energy variation of the printhead printing surface, both of which cause spreading or partial coating of the inks around the nozzle area and cause subsequent drop ejections to be misdirected, thereby reducing accuracy and product quality.
While known compositions and processes are suitable for creating printed products, such as marks (words, images and the like) on paper using inkjet printing techniques, due to the sensitivity limitation of human eyes, these conventional images can tolerate an accuracy variability (the difference between the printed product and the original pattern design, or “offset”) of about 40 μm from the intended print target. However, for printed electronic applications, higher printing accuracy is required. Printed electronic applications require an accuracy variability of below about 10 μm, such as below about 5 μm. Therefore, a need remains for improvements in ink printing systems, such as improvement in jetting accuracy. One challenge is related to energy variations on the printhead surface and ink accumulation on the printhead surface and around the printing orifice. The energy variations may cause misdirectional deposition of functional ink, resulting in poor jetting accuracy and unacceptably high offset.